In the wireless communication, the communication system adopting such MIMO has prevailed over the relevant market, so that the MIMO itself comes to be no novel to the persons skilled in the art. However, the communication system adopting the MIMO has been centered on a mobile communication, but has not been applied for a fixed communication to date. With the radio waves propagation line in a mobile communication, the fact is that the radio waves arrived from a transmitting antenna are subjected to reflections and scatterings by the surrounding landforms and as such so as to be received in a receiving apparatus with a collective group of constitutent waves. Thus, it is rich scattering resulting from such fact that always hinders a high-quality communication from being realized. The MIMO adopted in a mobile communication was epoch-making in that such rich scattering was reconsidered as the environmental resources to extract the potential inherent in the radio waves propagation in a mobile communication system instead of having been regarded as nuisance.
Against the doubts arising from what's happened when such MIMO communication system is applied to a line-of-sight fixed wireless communication in which a radio waves propagation channel is deterministic, there is disclosure in NPL 1 below on a line-of-sight MIMO applied thereto, though the number of such examples is smaller than those applied to a mobile communication system.
In such mobile communication system, a communication channel is regarded as a probabilistic matrix (or simply referred to as matrix) whereas it is required that such communication channel be deterministically handled in the line-of-sight fixed communication system.
In NPL 1 below, there is disclosure that the conditions expressed with the following formula are imposed on the communication channel matrix H by enlarging the antenna-to-antenna spacing at both of the transmitting and receiving sides, in which n denotes the number of antennas.H·HH=n·In  {Formula 1}In this regard, the phase rotation of the signal is feasible with linear antennas as verified by the following formula 2 for the transmitting antenna number i and the receiving antenna number k which are linearly disposed such that they are opposed to each other between transmission and reception.
                              π          n                ·                              [                          ⅈ              -              k                        ]                    2                                    {                  Formula          ⁢                                          ⁢          2                }            For instance, when n is equal to 2, the communication channel matrix H is defined as the following formula 3.
                              H          max                =                  [                                                    1                                            j                                                                    j                                            1                                              ]                                    {                  Formula          ⁢                                          ⁢          3                }            
Thus, the antennas arrangement satisfying the conditions of the formula 1 is feasible. In NPL 1, there is disclosure that the communication channel capacity according to the MIMO communication system is maximized by Hmax when the conditions of the formula 1 are satisfied.
In other words, not in the mobile environment entailing reflections and scatterings, but even in the deterministic line-of-sight communication environment, the increase of communication channel capacity in the MIMO communication system is feasible.
The case where such deterministic line-of-sight MIMO communication system is applied to a small-scale fixed microwaves communication is discussed herein. Generally speaking, for such small-scale microwaves communication, the frequency band ranging from several GHz to several-tens GHz is employed, which corresponds to several mm to several cm in terms of wavelengths. Accordingly, the movement of the antennas orientation whose sensitivity is high against such subtle climate conditions as the wind, the surrounding temperature and so forth causes a serious phase rotation. Under such conditions, it is hard to ensure the aforesaid definitive communication channel matrix.
To note, in the theoretical analysis mentioned below, it is analytically shown that there is no change in communication channel capacity for the aforesaid capacity enlargement even when the displacement of the orientation of such high sensitive antennas might happen.
With the MIMO communication system, plural independent signals are transmitted/received at the same time in the same frequency band. Thus, it requires that the signals be separated and detected accordingly. As one of the means to satisfy such requirement, there is a method according to matrix operation (hereinafter, abbreviated as ‘SVD system’) employing a unitary matrix obtained by singular value decomposition (hereinafter, abbreviated as ‘SVD’). In such SVD system, provided that the feedback data for constructing the unitary matrix is delivered from the receiving end to the transmitting end in an ideal manner, even when the displacement of the orientation of such highly sensitive antennas might happen as described above, the unitary matrix acts to compensate for such displacement. As the result of it, the large capacity fixed microwaves communication is realized according to the MIMO communication system.
However, such feedback data not only increases overheads, but also requires reverse links.
To note, with the modeling of the communication channel matrix H described below, analysis is made inclusive of the displacement of the orientation of such high sensitive antennas.
By the way, upon subjecting the aforesaid line-of-sight fixed communication channel in which a propagation channel is deterministic to the singular value analysis, there is a position between antennas where a singular point arises with a eigenvalue rendered into a geometric multiplicity (double eigenvalue or multiple eigenvalue). Such singular value is uniquely specified, but singular vectors are not so. In particular, such singular states are analytically bothersome, by which there are some cases where the serious transition of such singular vectors might arise.
To note, on the contrary, making use of such phenomenon allows various arrangements to be available. As for various types of exemplified arrangements making the most of such phenomenal characteristics, they are explained in details at the later stage.
Further, as one of the big problems with the deterministic line-of-sight MIMO communication system, it requires that carrier synchronization be made between antennas at the transmitting side or the receiving side according to the aforesaid conventional method. In other words, it requires that the phase among plural antennas at the transmitting side or the receiving side be the same or arranged with a certain difference in phase among them.
On the other hand, with a fixed microwaves communication system, it requires that the antenna-to-antenna spacing be widened in view of the frequencies to be handled. Accordingly, the respective radios including a local oscillator are disposed near the antennas. In other words, the problem with the carrier synchronization among the antennas becomes large constraint to construct the fixed microwaves communication system.